This invention relates to a crash barrier of the type designed to be positioned alongside a roadway to decelerate an impacting vehicle in a controlled manner.
Crash barriers of the general type described above have been designed utilizing a wide variety of energy-absorbing materials. For example, U.S. Pat. Nos. 4,452,431 and 3,503,600 disclose energy-absorbing devices using water-filled containers. The devices disclosed in U.S. Pat. No. 4,352,484 use honeycomb material which is filled with foam and which operates by compressing the foam and causing adjacent layers of honeycomb material to cut into one another. U.S. Pat. No. 4,399,980 discloses another system using bendable tubes positioned between diaphragms, and U.S. Pat. No. 4,635,981 discloses metal columns reinforced with foam. U.S. Pat. No. 4,711,481 discloses metal column cross braced with plates or straps to reduce buckling.
Meinzer, U.S. Pat. No. 4,321,989, discloses a crash barrier having an array of bays, each containing an element that is filled with an energy-absorbing foam (FIGS. 4 and 5). A wire mesh basket is positioned inside the foam element to contain the foam within the basket to prevent portions of the foam from escaping as the element is crushed. Somewhat similarly, Ivy, U.S. Pat. No. 4,909,661, discloses a crash barrier having an upper portion formed of a collapsible material in which is embedded a wire mesh reinforcement of the type shown in FIGS. 18 and 19.
The approaches described in the above-identified patents are characterized by a number of disadvantages. In many cases, the column stability of the energy-absorbing element is low. Often expensive and sometimes bulky frameworks are required to prevent the crash barrier (which has a substantial length) from buckling in an undesirable manner during an impact. Some of the devices described above appear to rely primarily on the compressible foam for energy-absorption. Note in particular that the reinforcing baskets shown in the Meinzer and Ivy patents appear to be of light gauge material which is not sufficiently rigid to cause deformation of the material to contribute any substantial fraction of the energy-absorbing capacity of the element. This is not surprising in view of the apparent use of the basket to retain the foam during an impact, and not to act as a principal energy-absorbing element. Another common disadvantage is that metal columns such as those disclosed in U.S. Pat. No. 4,635,981 will often tend to fail in a buckling mode, in which a relatively small fraction of the metal is strained, often to a relatively small degree. This represents an inefficient use of the metal in the energy absorbing elements, and such inefficiency results in a lower energy absorption capacity than would be possible if a greater proportion of the metal were strained to a greater degree.
It is accordingly an object of this invention to provide a crash barrier that provides improved column stability such that the need for bracing frameworks is reduced or eliminated, that provides improved efficiency by straining a large volume of rigid components to a large extent, that is readily adapted to advanced designs which are intended both to redirect an axially impacting vehicle as well as to slow it, and that can be implemented in a lightweight, low-cost form that is relatively compact and well-suited for use in situations where limited space is available for a crash barrier.